Two and half months is not that old in the grand scheme of things. I have started yeast off of refrigerated slants that were two years old.
At 50% viability, the average Wyeast Activator pack has 50 billion viable yeast cells. The maximum cell density for a liquid culture is 200 million yeast cells per milliliter, which means that the maximum cell density for a 1L culture is 200 billion yeast cells.
The biggest mistake that amateur brewers make when making a starter is treating it like a small batch of beer. The goal of a starter is to increase yeast biomass, not produce ethanol. If possible, we want to pitch the culture just as the deceleration phase meets the stationary phase. That's the point where no additional biomass growth occurs. From that point forward, reproduction only occurs in response to cell death and cell health begins to decline.
![](http://i699.photobucket.com/albums/vv356/tonestack/Brewing/YeastGrowthCurve_zpsb66047c5.jpg)
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Ideally, a 1L yeast culture should be pitched 12 to 18 hours after inoculation in order to ensure peak cell health. Yeast cells divide every ninety minutes after exiting the lag phase. Assuming 50% viability, the cells from a Wyeast smack pack only need to divide twice in order to reach maximum cell density under perfect conditions. However, under real-world conditions, we have to factor cell death and less than optimal growth conditions.